A cartridge for supplying printing material is mounted in a printer. Disclosed in patent document 1 is a semi-sealed type cartridge equipped with a chamber for which the capacity can vary using a flexible film, a spring for biasing the flexible film to make the chamber interior a negative pressure, an air introduction port for introducing air into the chamber, and a valve section provided to the air introduction port. With this kind of semi-sealed type cartridge, when the printing material inside the chamber is consumed to a certain degree, the valve section opens, and air is introduced into the chamber from the air introduction port. As a result, the negative pressure inside the chamber is inhibited from becoming excessively large, and having printing material remain inside the chamber is suppressed. For example, see Unexamined Patent Publication No. 2011-140189.